We are studying the structures of three antibodies the Fab of humanized OKT4A, and two metal-binding mutants of the single-chain Fv of the catalytic antibody 43C9. Computational models of the antigen binding regions of all three antibodies have been constructed and will be compared to the crystal structures to ascertain the predictive power of the modeling techniques. High resolution structures will be needed to clearly define the mechanisms and properties of antigen binding by these proteins.